The main reason for Australia having unusual animals was its isolation from other countries. For millions of years the Australian continent was so far away from any other landmass that there was no possibility for new forms of animals to get to it.
How Did Australia Become So Isolated? A Story of Continental Drift
Up until about 250 millions of years ago the world had just one huge super-continent called Pangaea. Animals and plants intermixed with each other on this huge single landmass.
About 200 million years ago this super-continent broke up into two continents — Laurasia and Gondwana. When this separation took place monotremes an marsupials were the predominate mammals of the Gondwana region and placental mammals in Laurasia.
Then about 60 million years ago Gondwana broke up into what became South America, Africa, Antarctica, India and Australia.
Australia and Antarctica slowly drifted southwards, far away from all the other continents, and became completed isolated from the rest of the world by vast oceans. The other continents however stayed relatively close to each other and over time collided or joined parts of the old Laurasia landmass. When these landmasses came together monotremes and marsupials were unable to compete with the more advanced placental mammals and became mostly extinct. In Africa and India marsupials became completely extinct. When South America joined North America almost all the marsupials there also vanished and were replaced by placental mammals.
Australia, meanwhile, drifted in a vast ocean, isolated from the rest of the world. The animals and plants which were originally on the Australian landmass no longer had contact with creatures from other parts of the world and continued to evolve independently. The climate also became drier and more arid. Monotremes and marsupials were more suitable for this new environment and became the dominate animals in Australia.
This separate evolution has resulted in some unusual and odd Australian animals. This is why Australian native animals are so different from those found elsewhere in the world.
It was once thought that marsupials originated in Australia. Recent fossil evidence and genetic research, however, suggests that they may in fact have originated in what is now modern-day China on the ancient landmass known as Pangaea.
About 200-180 million years ago Pangaea broke up into two continents Laurasia with North America, Europe, China and parts of Asia and Gondwana with South America, Africa, Antarctica, Australia and India. (diagram left).
Marsupials are believed to have arrived in Australia around 50 million years ago via North America, South America and through Antarctica.
Once Australia separated from the other continents and started to drift southward the marsupials stranded on it didn't have any competition from placental mammals. Without competition the marsupials diverged into over 235 different species found in Australia today. Some descendants of those original marsupials even almost hopped their way back towards China reaching as far as Indonesia and Papua New Guinea.
Unfortunately the original marsupials in other parts of the world couldn't compete with placental mammals and became mostly extinct. A few marsupials still survive in North and South America.
Australia's long isolation from the rest of the world has allowed Australian animals to evolve separately from those in other parts of the world, but to fill similar niches in the environment. For example the Echidna is an Australian Anteater. The Tasmanian Tiger (now extinct) was a marsupial wolf. The existence of similar animals in different parts of the world is referred to as "Parallel Evolution".
There are three types of mammals in Australia. These are monotremes, marsupials and placentals.
Monotremes first appeared between 145–99 million years ago and are the oldest type of Australian mammals. Two out of the five known species of monotremes in the world live in Australia. These are the Echidna and Platypus.
Marsupials appeared about 64-65 million years ago and are the second oldest type of mammal found in Australia. They occupy every niche of the Australian habitat and range from the large Red Kangaroo to marsupials of the smaller than a mouse.
Placental mammals are relatively recent arrivals to Australia. Bats were the first to arrive getting here about 23 million years ago. Rodents arrived about 5-10 million years ago. These animals reached Australia by flying and crossing the seas that separated Australian from Asia when Australia slowly stated drifting closer to Asia making crossings to the continent possible. These placental mammals make up a very small percentage of the total mammalian population. Humans introduced a number of animals. The Dingo was the first of these, coming here about 5,000 years ago.
Did You Know
Australia does not have any native monkeys or apes. This is another result of its isolations from other continents.
Australia has many amphibians and reptiles found nowhere else in the world.
Lizards – There are over 700 species unique to Australia alone.
Snakes – Australia has more poisonous snakes than non-poisonous ones. The Red-bellied Black Snake is one.
Frogs – Four families of native frogs inhabit the continent.
Crocodiles – Australia has two species of crocodile. The Saltwater Crocodile is the world's largest and can grow to 1,000 kilos and is known to attack humans. Fresh water crocodiles are much smaller and do not attack humans.
Turtles – There are 35 species of freshwater turtles. Six species of sea turtle also visit the coastlines.
Australia has 800 species of birds, 350 are found only in Australasia.
Megapods – as the Mallee fowl, trace their ancestry as far back as Gondwanan time. These birds are stocky birds which look somewhat like chickens. They have small heads and large feet (that's why the name "megapod" meaning big-feet).
Other birds such as Kookaburras are the world's largest kingfishers.
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The Outback is vast and breathtakingly beautiful.
Waltzing Matilda is Australia's favorite song.